Molecular changes in Nef with progression to AIDS. We have compared nef gene sequences isolated by polymerase chain reaction from peripheral blood lymphocyte DNA of macaques which had been inoculated with either the biologically or molecularly cloned simian immunodeficiency virus, SIV/Mne. Samples from each animal obtained either early (weeks 2-8) or after significant CD4+ depletion (weeks 21-137) after infection were analyzed. Five substitutions in the predicted Nef amino acid sequence were seen in all animals at the late time points. Animals inoculated with virus already containing the "late version" nef gene developed a more aggressive disease. We propose to build chimeric viruses of the molecular clone of SIV/Mne that contain the late nef gene sequence that is associated with AIDS. The effects of the changes in nef on functions which can be assayed in vitro such as CD4 downregulation, infectivity and protein interactions will be examined. Macaques will also be infected with this clone as well as with the wild-type clone in order to examine the in vivo pathogenicity of the new nef construct.